Sinterable bioceramics and method of manufacturing the same

ABSTRACT

The present invention discloses a method that can improve the sintering ability of calcium sulfate. The material can be used as a bio-material. This method is prepared by pre-mixing +1 and/or +2 and/or +3 and/or +4 and/or +5 valence element and/or its chemical compounds which serves as a sintering additive to calcium sulfate. During sintering, the sintering additive may form a compound and/or a glass and/or a glass-ceramic to assist the densification of the calcium sulfate. The strength and biocompatibility of the specimen after sintering are satisfactory.

This application claims priority of No. 098100973 filed in Taiwan R.O.C.on Jan. 12, 2009 and priority of No. 098125273 filed in Taiwan R.O.C. onJul. 28, 2009 under 35 USC 119, the entire contents of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to calcium sulfate based biomaterials, andmethods for making such materials. These materials can be used as bonesubstitutes. In particular, the strength of the calcium sulfate addedwith sintering additives after firing is satisfactory. In addition,these materials show good biocompatibility.

2. Related Art

The volume and weight of the bones occupy the most parts of human'sbody. The main function of bones is to assist our bodies to take actionand to support the body structure. As the flaw or damage is formed inbones, the clinical treatment is often required. The reasons causingsuch serious damages on bones are bone fractures, or bone tumor, orosteomyelitis, or collapses of vertebra, or the flawed hip bone, or thefailed artificial joint. In order to resolve these damages, to replacethe damaged bone with bone graft is still a common treatment in theclinics.

Nowadays, the bone graft comes from autograft and allograft. Autograftmeans the transplantation of organs, tissues or even proteins from onepart of the body to another part in the same individual. This is arather safe treatment. It may induce a good recovery. However, thesource of autograft is limited. In addition, the elders, children orpeople who are not healthy are not suitable for such autografttreatment. Allograft means the transplantation of cells, tissues, ororgans, sourced from the same species of a genetically non-identicalhuman body. The bone graft in allograft may come from the bone bank.However, the quality of bones is questionable. For example, the disease,such as AIDS or hepatitis etc., may come with the surgery. In order toavoid the limitation and risk of autograft and allograft, using theartificial bone substitutes is becoming a popular alternative. Manymedical companies in the world have therefore put their attention ondeveloping bone substitutes.

The first bone graft was generated from Netherlands, by JobVan Meekrenin 1668. In the 19^(th) century, many doctors cured the fractures anddamages of bones by using autograft. The results of surgeries were verysuccessful. Till now, the technology of autograft is not changed toomuch, compared with that developed 100 hundred years ago.

Polymeric bone cement has been used as filler in orthopedics for quite awhile. Since 1960, polymethylmethacrylate acid has been used to fillinto the cavity between the artificial joint and bone tissue. It can fixthe artificial joint in the bone tissue. Such bone cement has goodfixing effect in the early stage; however, after implanting for a longtime, the implanted component becomes loose because of stress shieldingand foreign body reaction. In addition, one more operation is oftenneeded to perform on 70% of the patient after implanting for 10 years.This circumstance results in wasting of money and inconvenience fordoctors and patients. Although the bone cement can avoid the soft tissueto grow into defects and holes of bones, it still cannot be absorbed byhuman's body. The bone cement also can not be transferred into bonetissue. Furthermore, the high temperature and residual monomer generatedduring mixing bone cement will cause the death and toxic pollution ofsurrounding tissue. Therefore, many medical teams intend to use theabsorbable bone substitutes, such as natural coral, hydroxyapatite,calcium phosphate, hemihydrate calcium sulfate or its mixture, toreplace the traditional bone cement.

Calcium sulfate is massively used as the shaping molds in ceramicindustry. The porous calcium sulfate can absorb water, but its strengthis low. Therefore, the service lifespan of calcium sulfate used as moldsis limited. If the strength of calcium sulfate can be improved, theservice time will be extended. In addition, the calcium sulfate can beused as bulks and films in orthopedics because it has goodbiocompatibility and bio-degradability. However, the application ofcalcium sulfate is limited because it cannot be sintered and itsstrength is thus low.

Nowadays, the calcium sulfate products are made at room temperature(without sintering/heat treatment). This is the reason why the strengthof calcium sulfate is poor after heat treatment. This is also the reasonwhy the amount of calcium sulfate products is used less than that ofcalcium phosphate products used in the medical area.

SUMMARY OF THE INVENTION

Hereby, the present invention discloses a sinterable calcium sulfate anda method of manufacturing the same. Some sintering additives are addedinto calcium sulfate to improve its sintering ability. The presence ofthese sintering additives should not affect the biocompatibility ofcalcium sulfate. The materials thus have appropriate strength andbiocompatibility after heat treatment, which can be used asbiomaterials.

This method is prepared by pre-mixing +1 and/or +2 and/or +3 and/or +4and/or +5 valence elements and/or their chemical compounds into calciumsulfate as sintering additives. The chemical compounds include oxidecompounds, non-oxide compounds, intermetallic compounds, amphotericcompound, metal-like compounds, stoichiometric compound,non-stoichiometric compounds, mixed-valence-state compounds, glass,glass-ceramics etc. During firing samples at or above the temperature of600° C., these sintering additives assist the densification of calciumsulfate. The strength and biocompatibility of specimens aresatisfactory. Thereby, these calcium sulfate-based ceramics can be usedas bone substitutes.

In the present invention, the sintering additives can be +1 and/or +2and/or +3 and/or +4 and/or +5 valence elements and/or their compounds,which can also form glass or glass-ceramic materials during sintering.The mixtures comprise calcium sulfate and 0.1 to 50 wt % sinteringadditives. The mixtures are shaped in the mold. During sintering atelevated temperatures, the sintering additives can form glass orglass-ceramic or compound to assist the densification of calciumsulfate. The calcium sulfate ceramics after sintering have the maximumcompressive strength of 183 MPa. These materials can be used as bonesubstitutes.

The traditional procedure of manufacturing glass is complex. Forexample: the glass starting materials (e.g. SiO₂, CaO, Na₂O etc.) arefirst heated up at the high temperature, and then quenched, ground andsieved. After that, the ceramic powder and glass are mixed together,shaped and fired. The glass or glass-ceramic specimens eventually can beobtained. However, the ceramics and glass starting materials aredirectly mixed together in the present invention. The mixture is thenshaped and fired. The specimens containing glass can also be madewithout using the above-mentioned complex pre-treatments. The sinteringadditives disclosed in the present invention can form glass orglass-ceramic by firing with calcium sulfate at elevated temperatures.Compared with the traditional method, it is much easier to prepare theglass or glass-ceramic specimens by using the method used in the presentinvention.

The scope and the applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, wherein:

FIG. 1 depicts the flowchart of the present invention;

FIGS. 2( a) to 2(d) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % silica, (c) calcium sulfate+10 wt %silica and (d) calcium sulfate+50 wt % silica specimens after firing at900° C.;

FIGS. 3( a) to 3(d) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % silica, (c) calcium sulfate+10 wt %silica and (d) calcium sulfate+50 wt % silica specimens after firing at1000° C.;

FIGS. 4( a) to 4(d) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % silica, (c) calcium sulfate+10 wt %silica and calcium sulfate+50 wt % silica specimens after firing at1100° C.;

FIGS. 5( a) to 5(d) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % silica, (c) calcium sulfate+10 wt %silica and (d) calcium sulfate+50 wt % silica specimens after firing at1200° C.;

FIGS. 6( a) to 6(c) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % silica and (c) calcium sulfate+50 wt% silica specimens after firing at 1300° C.;

FIGS. 7( a) to 7(e) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+5 wt % silica+9.5 wt % sodium hydrogencarbonate, (c) calcium sulfate+5 wt % silica+9.5 wt % calcium oxide, (d)calcium sulfate+5 wt % silica+9.5 wt % aluminum oxide and (e) calciumsulfate+5 wt % silica+9.5 wt % zirconium dioxide specimens after firingat 900° C.;

FIGS. 8( a) to 8(e) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+5 wt % silica+9.5 wt % sodium hydrogencarbonate, (c) calcium sulfate+5 wt % silica+9.5 wt % calcium oxide, (d)calcium sulfate+5 wt % silica+9.5 wt % aluminum oxide and (e) calciumsulfate+5 wt % silica+9.5 wt % zirconium dioxide specimens after firingat 1000° C.;

FIGS. 9( a) to 9(e) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+5 wt % silica+9.5 wt % sodium hydrogencarbonate, (c) calcium sulfate+5 wt % silica+9.5 wt % calcium oxide, (d)calcium sulfate+5 wt % silica+9.5 wt % aluminum oxide and (e) calciumsulfate+5 wt % silica+9.5 wt % zirconium dioxide specimens after firingat 1100° C.;

FIGS. 10( a) to 10(d) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+5 wt % silica+9.5 wt % calcium oxide, (c)calcium sulfate+5 wt % silica+9.5 wt % aluminum oxide and (d) calciumsulfate+5 wt % silica+9.5 wt % zirconium dioxide specimens after firingat 1200° C.;

FIGS. 11( a) to 11(d) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+5 wt % silica+9.5 wt % calcium oxide, (c)calcium sulfate+5 wt % silica+9.5 wt % aluminum oxide and (d) calciumsulfate+5 wt % silica+9.5 wt % zirconium dioxide specimens after firingat 1300° C.;

FIGS. 12( a) and 12(b) respectively depict the photographs of (a)calcium sulfate and (b) calcium sulfate+1 wt % sodium hydrogencarbonate+5 wt % silica+9.4 wt % calcium oxide specimens after firing at1100° C.;

FIG. 13 depicts the SEM micrograph of the specimen after firing at 1100°C., wherein the specimen comprises calcium sulfate+1 wt % sodiumhydrogen carbonate+5 wt % silica+9.4 wt % calcium oxide;

FIGS. 14( a) and 14(b) respectively depict the photographs of (a)calcium sulfate, (b) calcium sulfate+0.15 wt % phosphorus pentoxide+0.26wt % calcium oxide+0.59 wt % silica specimens after firing at 1100° C.;

FIGS. 15( a) to 15(d) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % starting materials of glass (SPCN),(c) calcium sulfate+10 wt % starting materials of glass (SPCN) and (d)calcium sulfate+50 wt % starting materials of glass (SPCN) specimensafter firing at 900° C., wherein SPCN is the combination of SiO₂, P₂O₅,CaO and NaHCO₃.

FIGS. 16( a) to 16(d) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % starting materials of glass (SPCN),(c) calcium sulfate+10 wt % starting materials of glass (SPCN) and (d)calcium sulfate+50 wt % starting materials of glass (SPCN) specimensafter firing at 1000° C.;

FIGS. 17( a) to 17(d) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % starting materials of glass (SPCN),(c) calcium sulfate+10 wt % starting materials of glass (SPCN) and (d)calcium sulfate+50 wt % starting materials of glass (SPCN) specimensafter firing at 1100° C.;

FIGS. 18( a) to 18(d) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % starting materials of glass (SPCN),(c) calcium sulfate+10 wt % starting materials of glass (SPCN) and (d)calcium sulfate+50 wt % starting materials of glass (SPCN) specimensafter firing at 1200° C.;

FIGS. 19( a) to 19(e) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % starting materials of glass (SP),(c) calcium sulfate+1 wt % starting materials of glass (SPN), (d)calcium sulfate+1 wt % starting materials of glass (SPC) and (e) calciumsulfate+1 wt % starting materials of glass (SPCN) specimens after firingat 900° C., wherein SP is the combination of SiO₂ and P₂O₅; SPN is thecombination of SiO₂, P₂O₅ and NaHCO₃; SPC is the combination of SiO₂,P₂O₅ and CaO; and SPCN is the combination of SiO₂, P₂O₅, CaO and NaHCO₃.

FIGS. 20( a) to 20(e) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % starting materials of glass (SP),(c) calcium sulfate+1 wt % starting materials of glass (SPN), (d)calcium sulfate+1 wt % starting materials of glass (SPC) and (e) calciumsulfate+1 wt % starting materials of glass (SPCN) specimens after firingat 1000° C.;

FIGS. 21( a) to 21(e) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate +1 wt % starting materials of glass (SP),(c) calcium sulfate+1 wt % starting materials of glass (SPN), (d)calcium sulfate+1 wt % starting materials of glass (SPC) and (e) calciumsulfate+1 wt % starting materials of glass (SPCN) specimens after firingat 1100° C.;

FIGS. 22( a) to 22(e) respectively depict the photographs of (a) calciumsulfate, (b) calcium sulfate+1 wt % starting materials of glass (SP),(c) calcium sulfate+1 wt % starting materials of glass (SPN), (d)calcium sulfate+1 wt % starting materials of glass (SPC) and (e) calciumsulfate+1 wt % starting materials of glass (SPCN) specimens after firingat 1200° C.;

FIGS. 23( a) and 23(b) respectively depict the photographs of (a)calcium sulfate and (b) calcium sulfate+14.5 wt % starting materials ofglass (SA) specimens after firing at 1100° C., wherein SA is thecombination of SiO₂ and Al₂O₃.

FIGS. 24( a) to 24(d) respectively depict the photographs of (a) calciumsulfate and (b) calcium sulfate+1 wt % silica, (c) calcium sulfate+10 wt% silica and (d) calcium sulfate+50 wt % silica specimens after firingat 1100° C.; and

FIG. 25 depicts the SEM micrograph of the specimen after firing at 1100°C., wherein the specimen comprises calcium sulfate+1 wt % startingmaterials of glass (SPCN).

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be apparent from the following detaileddescription, which proceeds with reference to the accompanying drawings,wherein the same references relate to the same elements.

Hereinafter, the present invention will be described more clearly asfollows.

The flowchart of preparation of sinterable bioceramics in the presentinvention is present in FIG. 1, and the method of manufacturing thesinterable calcium sulfate ceramic material includes the steps S1 to S4.

In the step S1, calcium sulfate is provided.

In the step S2, a sintering additive is mixed with the calcium sulfateto prepare a mixture.

In the step S3, the mixture is shaped in a mold to form a sample (orproduct).

In the step S4, the sample (or product) is fired at the temperatureranging from 600° C. to 1400° C. to obtain the calcium sulfate ceramicmaterial. Hence, the sintered calcium sulfate ceramic material includesor consists of the calcium sulfate and the sintering additive. Thesintering temperature is above 600° C. The optimum sintering temperatureis 800° C., 1000° C., 1200° C. or 1400° C.

The sintering additive used in the present invention is selected fromthe group consisting of a +1 valence element and its compound, a +2valence element and its compound, a +3 valence element and its compound,a +4 valence element and its compound and a +5 valence element and itscompound. That is, the sintering additive is selected from the +1 and/or+2 and/or +3 and/or +4 and/or +5 valence elements and/or their chemicalcompounds. The amount of the sintering additive in the mixture is in arange of 0.1 wt % to 50 wt %. The better amount of sintering additive isin a range of 0.5 wt % to 50 wt %; and the optimum amount of sinteringadditive is in a range of 0.5 wt % to 15 wt %. After sintering, thecalcium sulfate ceramic material has the optimum flexural strength ofabout 90 MPa and compressive strength of about 183 MPa.

Hereinafter, a method of the present invention that can improve thesintering ability of calcium sulfate by adding +1 and/or +2 and/or +3and/or +4 and/or +5 valence elements and/or their chemical compounds isdisclosed according to the following examples.

Examples 1 to 6

The materials used in these EXAMPLES were calcium sulfate (CaSO₄) powderand +4 valence chemical compounds (e.g. silica, SiO₂). First, thecalcium sulfate and silica powders were mixed together uniformly. Theamounts of silica were 1 wt %, 10 wt % and 50 wt %. The mixed powderswere consolidated into discs of 25.4 mm diameter and 3 mm thickness.These disc samples were sintered at 900° C. to 1300° C. for 3 hours. Thedensities of samples were recorded after sintering, as shown in theTable 1.

TABLE 1 CaSO₄ + CaSO₄ + CaSO₄ + 1 wt % 10 wt % 50 wt % CaSO₄ SiO₂ SiO₂SiO₂ EXAMPLE 1  25° C. 2.1 1.5 1.7 1.5 density (g/cm³) EXAMPLE 2  900°C. / 1.6 1.5 1.4 density (g/cm³) EXAMPLE 3 1000° C. / 2.0 1.6 1.5density (g/cm³) EXAMPLE 4 1100° C. / 2.7 1.6 1.9 density (g/cm³) EXAMPLE5 1200° C. / 2.6 1.5 1.5 density (g/cm³) EXAMPLE 6 1300° C. / 2.2 / 1.5density (g/cm³) /: The density of samples cannot be measured due tocollapse of the samples.

Hereinbefore, the EXAMPLES show that the density of calcium sulfate(CaSO₄) increases after the suitable heat treatment. It indicates thatthe sintering ability of calcium sulfate can be improved by addingvarious amounts (1 wt %, 10 wt % and 50 wt %) of +4 valence chemicalcompounds (e.g. silica, SiO₂).

Example 7

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 2. The samples were fired at 900° C.for 3 hours. The photographs of samples are shown in FIGS. 2( a) to2(d).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith the +4 valence compounds (e.g. SiO₂) exhibit better sinteringability during the heat treatment. The amounts of +4 valence compoundsare 1 wt %, 10 wt % and 50 wt %. After the heat treatment, the calciumsulfate samples added with the +4 valence compound still hold theirshapes. However, the calcium sulfate without the additives collapsesafter the heat treatment (see FIG. 2( a)). It indicates that thesintering ability of calcium sulfate can be improved by adding variousamounts (1 wt %, 10 wt % and 50 wt %) of +4 valence chemical compounds(e.g. silica, SiO₂).

Example 8

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 3. The samples were fired at 1000°C. for 3 hours. The photographs of samples are shown in FIGS. 3( a) to3(d).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith the +4 valence compounds (e.g. SiO₂) exhibit improved sinteringability during the heat treatment. The amounts of +4 valence compoundsare 1 wt %, 10 wt % and 50 wt %. After the heat treatment, the calciumsulfate samples added with the +4 valence compound still hold theirshapes. However, the calcium sulfate without the additives collapsesafter the heat treatment (see FIG. 3( a)). It indicates that thesintering ability of calcium sulfate can be improved by adding variousamounts (1 wt %, 10 wt % and 50 wt %) of +4 valence chemical compounds(e.g. silica, SiO₂).

Example 9

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 4. The samples were fired at 1100°C. for 3 hours. The photographs of samples are shown in FIGS. 4( a) to4(d).

Hereinbefore, the example shows that the sintering ability of calciumsulfate samples is improved after adding the +4 valence compounds (e.g.SiO₂) and after the heat treatment. The amounts of +4 valence compoundsare 1 wt %, 10 wt % and 50 wt %. After the heat treatment, the calciumsulfate samples added with the +4 valence compound still hold theirshapes. However, the calcium sulfate without the additives collapsesafter the heat treatment (see FIG. 4( a)). It indicates that thesintering ability of calcium sulfate can be improved by adding variousamounts (1 wt %, 10 wt % and 50 wt %) of +4 valence chemical compounds(e.g. silica, SiO₂).

Example 10

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 5. The samples were fired at 1200°C. for 3 hours. The photographs of samples are shown in FIGS. 5( a) to5(d).

Hereinbefore, the example shows that the sintering ability of calciumsulfate samples is improved after adding the +4 valence compounds (e.g.SiO₂) and the heat treatment. The amounts of +4 valence compounds are 1wt %, 10 wt % and 50 wt %. After the heat treatment, the calcium sulfatesamples added with the +4 valence compound still hold their shapes.However, the calcium sulfate without the additives collapses after theheat treatment (see FIG. 5( a)). It indicates that the sintering abilityof calcium sulfate can be improved by adding various amounts (1 wt %, 10wt % and 50 wt %) of +4 valence chemical compounds (e.g. silica, SiO₂).

Example 11

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 6. The samples were fired at 1300°C. for 3 hours. The photographs of samples are shown in FIGS. 6( a) to6(c).

Hereinbefore, the example shows that the sintering ability of calciumsulfate samples is improved after adding the +4 valence compounds (e.g.SiO₂) and the heat treatment. The amounts of +4 valence compounds are 1wt % and 50 wt %. After the heat treatment, the calcium sulfate samplesadded with the +4 valence compound still hold their shapes. However, thecalcium sulfate without the additives collapses after the heat treatment(see FIG. 6( a)). It indicates that the sintering ability of calciumsulfate can be improved by adding various amounts (1 wt % and 50 wt %)of +4 valence chemical compounds (e.g. silica, SiO₂).

Examples 12 to 16

The disc samples for these EXAMPLES of the present invention wereprepared using the same methods as in EXAMPLES 2 to 6. The samples werefired at 900° C. to 1300° C. for 3 hours. The samples were then groundto obtain flat surfaces. The flexural strength of disc samples wasmeasured by using the biaxial 4-ball bending test (instrument: MTS810,MTS Co., USA) at the room temperature. The displacement rate was 0.48mm/min. The flexural strength of samples is presented in the Table 2.

TABLE 2 CaSO₄ + 1 CaSO₄ + 10 wt CaSO₄ + 50 wt CaSO₄ wt % SiO₂ % SiO₂ %SiO₂ EXAMPLE  900° C./flexural / 3.1 2.8 8.9 12 strength (MPa) EXAMPLE1000° C./flexural / 17.0 7.5 26.0 13 strength (MPa) EXAMPLE 1100°C./flexural / 41.0 12.9 39.1 14 strength (MPa) EXAMPLE 1200° C./flexural/ 26.1 22.2 90.4 15 strength (MPa) EXAMPLE 1300° C./flexural / 17.0 /81.1 16 strength (MPa) /: The flexural strength of samples cannot bemeasured due to the collapse of the samples.

Hereinbefore, the EXAMPLES show that the flexural strength of purecalcium sulfate (CaSO₄) cannot be measured owing to the collapse ofsamples. It indicates that the pure calcium sulfate cannot be sinteredby using only the heat treatment. However, the flexural strength of theCaSO₄ samples added with the +4 valence compound (e.g. SiO₂) increasesafter the heat treatment. The amounts of +4 valence compounds are 1 wt%, 10 wt % and 50 wt %. For certain condition, the flexural strength ofsamples is about 90 MPa. It indicates that the sintering ability ofcalcium sulfate can be improved by adding various amounts (1 wt %, 10 wt% and 50 wt %) of +4 valence chemical compounds (e.g. silica, SiO₂).

Hereinbefore, the EXAMPLES present that only one element or its compoundis added into the calcium sulfate. Hereinafter, the EXAMPLES show thattwo kinds of sintering additives also can be added into calcium sulfateto improve the sintering ability of calcium sulfate. All the materialsused in the following EXAMPLES of the present invention are calciumsulfate (CaSO₄) powder, +1 valence compound (e.g. sodium hydrogencarbonate, NaHCO₃), +2 valence compound (e.g. calcium oxide, CaO), +3valence compound (e.g. aluminum oxide, Al₂O₃) and +4 valence compound(e.g. zirconium oxide, ZrO₂ and silica, SiO₂). The two kinds ofsintering additives are chosen from any +1 and/or +2 and/or +3 and/or +4and/or +5 valence chemical compounds. The chemical compounds mentionedhereinbefore can be prepared by heating up the elements in air.

Examples 17 to 22

The preparation steps for samples in EXAMPLE 17 to 22 are shown below.Firstly, calcium sulfate (CaSO₄) was mixed uniformly with 5 wt % SiO₂and +1 valence chemical compound (e.g. NaHCO₃) or +2 valence chemicalcompound (e.g. CaO) or +3 valence chemical compound (e.g. Al₂O₃) or +4valence chemical compound (e.g. ZrO₂) respectively. The mixed powderswere consolidated into discs of 25.4 mm diameter and 3 mm thickness.These disc samples were sintered at 900° C. to 1300° C. for 3 hours. Thedensities of samples were recorded after sintering, as shown in theTable 3.

TABLE 3 CaSO₄ + 5 wt CaSO₄ + 5 wt CaSO₄ + 5 wt % SiO₂ and CaSO₄ + 5 wt %SiO₂ % SiO₂ 9.5 wt % % SiO₂ and and 9.5 wt % and 9.5 wt CaSO₄ NaHCO₃ 9.5wt % CaO Al₂O₃ % ZrO₂ EXAMPLE  25° C. 2.1 1.5 1.5 1.7 1.7 17 density(g/cm³) EXAMPLE  900° C. / 2.0 1.2 1.5 1.6 18 density (g/cm³) EXAMPLE1000° C. / 2.0 1.3 1.7 1.7 19 density (g/cm³) EXAMPLE 1100° C. / 2.5 1.81.7 1.8 20 density (g/cm³) EXAMPLE 1200° C. / / 2.2 1.7 1.9 21 density(g/cm³) EXAMPLE 1300° C. / / 2.0 1.5 1.6 22 density (g/cm³) /: Thedensity of samples cannot be measured due to the collapse of thesamples.

Hereinbefore, the EXAMPLES show that the density of calcium sulfate(CaSO₄) increases after the suitable heat treatment. It indicates thatafter the heat treatment, the sintering ability of calcium sulfate canbe improved by adding any two kinds of sintering additives selected from+1 and/or +2 and/or +3 and/or +4 valence compounds.

Example 23

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 18. The samples were CaSO₄ added 5wt % SiO₂ and 9.5 wt % NaHCO₃, CaSO₄ added 5 wt % SiO₂ and 9.5 wt % CaO,CaSO₄ added 5 wt % SiO₂ and 9.5 wt % Al₂O₃, CaSO₄ added 5 wt % SiO₂ and9.5 wt % ZrO₂ respectively. These samples were fired at 900° C. for 3hours. The photographs of samples are shown in FIGS. 7( a) to 7(e).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith any two kinds of sintering additives exhibit improved sinteringability during the heat treatment. These two kinds of additives areselected form +1 valence compounds (e.g. NaHCO₃) or +2 valence compounds(e.g. CaO) or +3 valence compounds (e.g. Al₂O₃) or +4 valence compounds(e.g. SiO₂, ZrO₂). After the heat treatment, the calcium sulfate samplesadded with the sintering additives still hold their shapes. However, thecalcium sulfate without the additives collapses after the heat treatment(see FIG. 7( a)). It indicates that the sintering ability of calciumsulfate can be improved by adding any two different kinds of additivesselected from +1 and/or +2 and/or +3 and/or +4 and/or +5 valencecompounds.

Example 24

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 19. The samples were CaSO₄ added 5wt % SiO₂ and 9.5 wt % NaHCO₃, CaSO₄ added 5 wt % SiO₂ and 9.5 wt % CaO,CaSO₄ added 5 wt % SiO₂ and 9.5 wt % Al₂O₃, CaSO₄ added 5 wt % SiO₂ and9.5 wt % ZrO₂ respectively. These samples were fired at 1000° C. for 3hours. The photographs of samples are shown in FIGS. 8( a) to 8(e).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith any two kinds of sintering additives exhibit improved sinteringability during the heat treatment. These two kinds of additives areselected form +1 valence compounds (e.g. NaHCO₃) or +2 valence compounds(e.g. CaO) or +3 valence compounds (e.g. Al₂O₃) or +4 valence compounds(e.g. SiO₂, ZrO₂). After the heat treatment, the calcium sulfate samplesadded with the sintering additives still hold their shapes. However, thecalcium sulfate without the additives collapses after the heat treatment(see FIG. 8( a)). It indicates that the sintering ability of calciumsulfate can be improved by adding any two different kinds of additivesselected from +1 and/or +2 and/or +3 and/or +4 valence and/or +5compounds.

Example 25

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 20. The samples were CaSO₄ added 5wt % SiO₂ and 9.5 wt % NaHCO₃, CaSO₄ added 5 wt % SiO₂ and 9.5 wt % CaO,CaSO₄ added 5 wt % SiO₂ and 9.5 wt % Al₂O₃, CaSO₄ added 5 wt % SiO₂ and9.5 wt % ZrO₂ respectively. These samples were fired at 1100° C. for 3hours. The photographs of samples are shown in FIGS. 9( a) to 9(e).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith any two kinds of sintering additives exhibit improved sinteringability during the heat treatment. These two kinds of additives areselected form +1 valence compounds (e.g. NaHCO₃) or +2 valence compounds(e.g. CaO) or +3 valence compounds (e.g. Al₂O₃) or +4 valence compounds(e.g. SiO₂, ZrO₂). After the heat treatment, the calcium sulfate samplesadded with the sintering additives still hold their shapes. However, thecalcium sulfate without the additives collapses after the heat treatment(see FIG. 9( a)). It indicates that the sintering ability of calciumsulfate can be improved by adding any two different kinds of additivesselected from +1 and/or +2 and/or +3 and/or +4 valence and/or +5compounds.

Example 26

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 21. The samples were CaSO₄ added 5wt % SiO₂ and 9.5 wt % CaO, CaSO₄ added 5 wt % SiO₂ and 9.5 wt % Al₂O₃,CaSO₄ added 5 wt % SiO₂ and 9.5 wt % ZrO₂ respectively. These sampleswere fired at 1200° C. for 3 hours. The photographs of samples are shownin FIGS. 10( a) to 10(d).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith any two kinds of sintering additives exhibit improved sinteringability during the heat treatment. These two kinds of additives areselected form +2 valence compounds (e.g. CaO) or +3 valence compounds(e.g. Al₂O₃) or +4 valence compounds (e.g. SiO₂, ZrO₂). After the heattreatment, the calcium sulfate samples added with sintering additivesstill hold their shapes. However, the calcium sulfate without theadditives collapses after the heat treatment (see FIG. 10( a)). Itindicates that the sintering ability of calcium sulfate can be improvedby adding any two different kinds of additives selected from +1 and/or+2 and/or +3 and/or +4 valence and/or +5 compounds.

Example 27

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 22. The samples were CaSO₄ added 5wt % SiO₂ and 9.5 wt % CaO, CaSO₄ added 5 wt % SiO₂ and 9.5 wt % Al₂O₃,CaSO₄ added 5 wt % SiO₂ and 9.5 wt % ZrO₂ respectively. These sampleswere fired at 1300° C. for 3 hours. The photographs of samples are shownin FIGS. 11( a) to 11(d).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith any two kinds of sintering additives exhibit improved sinteringability during the heat treatment. These two kinds of additives areselected form +2 valence compounds (e.g. CaO) or +3 valence compounds(e.g. Al₂O₃) or +4 valence compounds (e.g. SiO₂, ZrO₂). After the heattreatment, the calcium sulfate samples added with the sinteringadditives still hold their shapes. However, the calcium sulfate withoutthe additives collapses after the heat treatment (see FIG. 11( a)). Itindicates that the sintering ability of calcium sulfate can be improvedby adding any two different kinds of additives selected from +1 and/or+2 and/or +3 and/or +4 valence and/or +5 compounds.

Examples 28 to 32

The disc samples for these EXAMPLES of the present invention wereprepared using the same methods as in EXAMPLES 18 to 22. The sampleswere fired at 900° C. to 1300° C. for 3 hours. The samples were thenground to obtain flat surfaces. The flexural strength of disc sampleswas measured by using the biaxial 4-ball bending test (instrument:MTS810, MTS Co., USA) at the room temperature. The displacement rate was0.48 mm/min. The flexural strength of samples is presented in the Table4.

TABLE 4 CaSO₄ + 5 wt CaSO₄ + 5 wt CaSO₄ + 5 wt CaSO₄ + 5 wt % SiO₂ + %SiO₂ + % SiO₂ + % SiO₂ + 9.5 wt % 9.5 wt % 9.5 wt % 9.5 wt % CaSO₄NaHCO₃ CaO Al₂O₃ ZrO₂ EXAMPLE  900° C./ / 44.7 / 2.8 2.9 28 flexuralstrength (MPa) EXAMPLE 1000° C./ / 66.5 1.7 9.7 5.1 29 flexural strength(MPa) EXAMPLE 1100° C./ / 80 15.9 19.6 15.5 30 flexural strength (MPa)EXAMPLE 1200° C./ / / 32 16.5 25.0 31 flexural strength (MPa) EXAMPLE1300° C./ / / 13.6 15.1 17.0 32 flexural strength (MPa) /: The flexuralstrength of samples cannot be measured due to the collapse of thesamples.

Hereinbefore, the EXAMPLES show that the flexural strength of purecalcium sulfate (CaSO₄) cannot be measured owing to the collapse ofsamples. It indicates that the pure calcium sulfate cannot be sinteredby using the heat treatment. However, the flexural strength of CaSO₄added with two different kinds of additives increases after firing at atemperature above 900° C. These two kinds of additives are selected form+1 valence compounds (e.g. NaHCO₃) or +2 valence compounds (e.g. CaO) or+3 valence compounds (e.g. Al₂O₃) or +4 valence compounds (e.g. SiO₂,ZrO₂). It also indicates that the sintering ability of calcium sulfatecan be improved by adding two kinds of compounds selected from +1 and/or+2 and/or +3 and/or +4 valence and/or +5 compounds.

Hereinafter, EXAMPLES reveal that the sintering ability of calciumsulfate can be improved by adding three kinds of additives. Thecombinations of three kinds of additives are selected from any +1 and/or+2 and/or +3 and/or +4 and/or +5 valence compounds. All the materialsused for the EXAMPLES are the calcium sulfate mixed with the compositeadditives. The three kinds of sintering additives are chosen from +1valence compound (NaHCO₃), +2 valence compound (CaO), +3 valencecompound (Al₂O₃), +4 valence compound (SiO₂) and +5 valence compound(P₂O₅).

Example 33

First, calcium sulfate (CaSO₄) was mixed uniformly with 1 wt % of +1valence chemical compound (NaHCO₃), 5 wt % of +4 valence chemicalcompound (SiO₂) and 9.4 wt % of +2 valence chemical compound (CaO). Themixed powders were formed into discs of 20 mm diameter and 5 mmthickness via gelcasting. These disc samples were sintered at 1100° C.for 3 hours. The densities of samples were recorded after sintering, asshown in the Table 5.

TABLE 5 CaSO₄ + 1 wt % NaHCO₃ + 5 wt % CaSO₄ SiO₂ + 9.4 wt % CaO EXAMPLE33 1100° C. / 1.7 density (g/cm³) /: The density of samples cannot bemeasured due to the collapse of the samples.

Hereinbefore, the EXAMPLE shows that the density of CaSO₄ added withsintering additives is increased after the addition of the sinteringadditives. It indicates that after the heat treatment, the sinteringability of calcium sulfate can be improved by adding NaHCO₃, SiO₂ andCaO. It also means that after the heat treatment, the sintering abilityof calcium sulfate can be improved by adding any three kinds ofsintering additives selected from +1 and/or +2 and/or +3 and/or +4and/or +5 valence compounds.

Example 34

The sample for this EXAMPLE of the present invention was prepared usingthe same method as in EXAMPLE 33. The compositions of samples were CaSO₄added 1 wt % NaHCO₃, 5 wt % SiO₂ and 9.4 wt % CaO. These samples werefired at 1100° C. for 3 hours. The photographs of samples are shown inFIGS. 12( a) and 12(b).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples withthe added NaHCO₃, SiO₂ and CaO additives exhibit improved sinteringability during the heat treatment. The sample added with the sinteringadditives still holds its shape after the heat treatment. However, thecalcium sulfate without the additives collapses after the heat treatment(see FIG. 12( a)). It indicates that the sintering ability of calciumsulfate can be improved by adding any three different kinds of additivesselected from +1 and/or +2 and/or +3 and/or +4 and/or +5 valencecompounds.

Example 35

The disc samples for these examples of the present invention wereprepared using the same methods as in EXAMPLE 33. The samples were firedat 1100° C. for 3 hours. The samples were then ground to obtain flatsurfaces. The flexural strength of the disc samples was measured byusing the biaxial 4-ball bending test (instrument: MTS810, MTS Co., USA)at the room temperature. The displacement rate was 0.48 mm/min. Theflexural strength of the samples is presented in the Table 6.

TABLE 6 CaSO₄ + 1 wt % NaHCO₃ + 5 wt CaSO₄ % SiO₂ + 9.4 wt % CaO EXAMPLE35 1100° C./ / 24.0 flexural strength (MPa) /: The flexural strength ofsamples cannot be measured due to the collapse of the samples.

Hereinbefore, the EXAMPLE shows that the flexural strength of purecalcium sulfate (CaSO₄) cannot be measured owing to the collapse ofsamples. It indicates that the calcium sulfate cannot be sintered byusing the heat treatment. However, the flexural strength of CaSO₄-basedsamples is increased via adding three different kinds of additives.These three kinds of additives are NaHCO₃, CaO and SiO₂. It alsoindicates that the sintering ability of calcium sulfate can be improvedby adding any three kinds of additives selected from +1 and/or +2 and/or+3 and/or +4 and/or +5 valence chemical compounds.

Example 36

The sample for this EXAMPLE of the present invention was prepared usingthe same method as in EXAMPLE 33. The compositions of samples were CaSO₄added with 1 wt % NaHCO₃, 5 wt % SiO₂ and 9.4 wt % CaO. These sampleswere fired at 1100° C. for 3 hours. The SEM micrograph of sample isshown in FIG. 13.

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith the NaHCO₃, SiO₂ and CaO additives exhibit the sintering abilityafter the heat treatment. It indicates that the sintering ability ofcalcium sulfate can be improved by adding three different kinds ofadditives selected from +1 and/or +2 and/or +3 and/or +4 and/or +5valence compounds.

Example 37

This EXAMPLE reveals that the sintering ability of calcium sulfate alsocan be improved by adding three kinds of additives. The combinations ofthree kinds of additives were selected from any +1 and/or +2 and/or +3and/or +4 and/or +5 valence compounds. All the materials used for theEXAMPLE were the calcium sulfate, +2 valence compound (CaO), +4 valencecompound (SiO₂) and +5 valence compound (P₂O₅). Firstly, the calciumsulfate was uniformly mixed with 0.59 wt % SiO₂, 0.15 wt % P₂O₅ and 0.26wt % CaO. The mixed powders were consolidated into cylinder samples of10 mm diameter and 10 mm height. These cylinder samples were sintered at1100° C. for 1 hour. The densities of samples were recorded aftersintering, as shown in the Table 7.

TABLE 7 CaSO₄ + 0.15 wt % P₂O₅ + 0.26 wt % CaO + CaSO₄ 0.59 wt % SiO₂EXAMPLE 1100° C. / 2.8 37 density (g/cm³) /: The density of samplescannot be measured due to the collapse of the samples.

Hereinbefore, the EXAMPLE reveals that after the heat treatment, thedensity of calcium sulfate is increased by adding SiO₂, P₂O₅ and CaO. Itmeans that calcium sulfate exhibits the sintering ability by addingSiO₂, P₂O₅ and CaO. It also indicates that the addition of threesintering additives, such as SiO₂, P₂O₅ and CaO, can assist thedensification of calcium sulfate.

Example 38

The sample for this EXAMPLE of the present invention was prepared usingthe same method as in EXAMPLE 37. The compositions of sample were CaSO₄added with 0.15 wt % P₂O₅, 0.26 wt % CaO and 0.59 wt % SiO₂. The samplewas fired at 1100° C. for 1 hour. The photographs of samples are shownin FIGS. 14( a) and 14(b).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith P₂O₅, CaO and SiO₂ additives exhibit the sintering ability afterthe heat treatment. The sample added with the sintering additives stillholds its shape after the heat treatment. However, the calcium sulfatewithout the additives collapsed after the heat treatment (see FIG. 14(a)). It indicates that the sintering ability of calcium sulfate can beimproved by adding any three different kinds of additives selected from+1 and/or +2 and/or +3 and/or +4 and/or +5 valence compounds.

Example 39

The cylinder sample for this EXAMPLE of the present invention wasprepared using the same method as in EXAMPLE 37. The compositions ofsample were CaSO₄ added with 0.15 wt % P₂O₅, 0.26 wt % CaO and 0.59 wt %SiO₂. The sample was made into cylinder of 10 mm diameter and 10 mmheight. The sample was fired at 1100° C. for 1 hour. The sample wasfirst ground to obtain a flat surface, and then the compressive strengthof cylinder samples was measured at room temperature by using theuniversal testing instrument (MTS810, MTS, USA). The displacement ratewas 0.96 mm/min during testing. The ratio of diameter to height is 1to 1. The compressive strength of samples is listed in the Table 8.

TABLE 8 CaSO₄ + 0.15 wt % P₂O₅ + 0.26 wt % CaSO₄ CaO + 0.59 wt % SiO₂EXAMPLE 1100° C./ / 151.9 39 compressive strength (MPa) /: Thecompressive strength of samples cannot be measured due to the collapseof the samples.

Hereinbefore, the example shows that the compressive strength of purecalcium sulfate (CaSO₄) cannot be measured owing to the collapse ofsamples. It indicates that the pure calcium sulfate cannot be sinteredby using the heat treatment. However, the compressive strength ofCaSO₄-based samples is increased via adding three different kinds ofadditives. These three kinds of additives are P₂O₃, CaO and SiO₂. Italso indicates that the sintering ability of calcium sulfate can beimproved by adding any three kinds of sintering additives selected from+1 and/or +2 and/or +3 and/or +4 and/or +5 valence chemical compounds.

In addition, the sintering additives used for the present invention arealso selected from +1 and/or +2 and/or +3 and/or +4 and/or +5 valencegroups, which can form glass materials after the heat treatment. Theglass materials mean that the materials are amorphous in structure. Suchmaterials can flow at elevated temperature. The amount of sinteringadditives in the mixtures is in the range of 0.1 wt % to 50 wt %. Themixtures are shaped in the molds. After the heat treatment, thecompressive strength of CaSO₄-based ceramic materials is about 152 MPa.

Hereinafter, EXAMPLES reveals that the sintering ability of calciumsulfate can be improved by adding +1 and/or +2 and/or +3 and/or +4and/or +5 valence sintering additives. These additives form glass duringfiring at elevated temperature.

Examples 40 to 44

All the materials used for these EXAMPLES of the present invention werecalcium sulfate (CaSO₄), +1 valence glass starting materials (e.g.sodium hydrogen carbonate, NaHCO₃), +2 valence glass starting materials(e.g. calcium oxide, CaO), +4 valence glass starting materials (e.g.silica, SiO₂) and +5 valence glass starting materials (e.g. phosphoruspentoxide, P₂O₅). First, CaSO₄ and glass starting materials were mixedtogether. The amounts of glass starting materials were 1 wt %, 10 wt %and 50 wt %. The mixed powders were consolidated into cylinders of 10 mmdiameter and 10 mm height. The glass starting materials are selectedfrom +1 valence glass starting materials (e.g. sodium hydrogencarbonate, NaHCO₃), +2 valence glass starting materials (e.g. calciumoxide, CaO), +4 valence glass starting materials (e.g. silica, SiO₂) and+5 valence glass starting materials (e.g. phosphorus pentoxide, P₂O₅).The compositions of 1 wt %, 10 wt % and 50 wt % glass starting materialsare listed in the Table 9.

TABLE 9 Compositions 1 wt % glass starting 0.56 wt % SiO₂ + 0.11 wt %materials, labeled as 1 wt % P₂O₅ + 0.21 wt % CaO + SPCN 0.12 wt %NaHCO₃ 10 wt % glass starting 5.61 wt % SiO₂ + 1.04 wt % P₂O₅ +materials, labeled as 10 wt % 2.13 wt % CaO + 1.23 wt % NaHCO₃ SPCN 50wt % glass starting 28.06 wt % SiO₂ + 5.18 wt % P₂O₅ + materials,labeled as 50 wt % 10.64 wt % CaO + 6.13 wt % NaHCO₃ SPCN

The samples were fired at 900° C. to 1200° C. for 1 hour. The densitiesof samples were recorded after firing, as shown in the Table 10.

TABLE 10 CaSO₄ + 50 wt CaSO₄ + 1 wt % CaSO₄ + 10 wt % % glass glassstarting glass starting starting materials (1 wt % materials (10 wt %materials (50 wt CaSO₄ SPCN) SPCN) % SPCN) EXAMPLE  25° C. 2.1 1.9 1.91.7 40 density (g/cm³) EXAMPLE  900° C. / 2.2 1.9 1.5 41 density (g/cm³)EXAMPLE 1000° C. / 2.7 2.3 1.6 42 density (g/cm³) EXAMPLE 1100° C. / 2.82.7 1.5 43 density (g/cm³) EXAMPLE 1200° C. / 2.5 2.6 1.6 44 density(g/cm³) /: The density of samples cannot be measured due to the collapseof the samples.

Hereinbefore, the EXAMPLES show that the density of calcium sulfate(CaSO₄) is increased after the suitable heat treatment. It indicatesthat after the heat treatment, the sintering ability of calcium sulfatecan be improved by adding various amounts of glass starting materials(SPCN). The amounts of glass starting materials are 1 wt %, 10 wt % and50 wt %. It indicates that the addition of various amounts of glassstarting materials can assist the densification of calcium sulfate.

Example 45

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 41. The sample was fired at 900° C.for 1 hour. The photographs of samples are shown in FIGS. 15( a) to15(d).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith 1 wt %, 10 wt % and 50 wt % glass starting materials (SPCN) exhibitimproved sintering ability during the heat treatment. The samples addedwith the sintering additives still hold their shapes after the heattreatment. However, the calcium sulfate without the glass startingmaterials collapses after the heat treatment (see FIG. 15( a)). Itindicates that the sintering ability of calcium sulfate can be improvedby adding various amounts (1 wt %, 10 wt % and 50 wt %) of glassstarting materials (SPCN). The glass starting materials are selectedfrom +1 and/or +2 and/or +3 and/or +4 and/or +5 valence compounds.

Example 46

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 42. The samples were fired at 1000°C. for 1 hour. The photographs of samples are shown in FIGS. 16( a) to16(d).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith 1 wt %, 10 wt % and 50 wt % glass starting materials (SPCN) exhibitimproved sintering ability during the heat treatment. The samples addedwith the sintering additives still hold their shapes after the heattreatment. However, the calcium sulfate without the glass startingmaterials collapses after the heat treatment (see FIG. 16( a)). Itindicates that the sintering ability of calcium sulfate can be improvedby adding various amounts (1 wt %, 10 wt % and 50 wt %) of glassstarting materials (SPCN). The glass starting materials are selectedfrom +1 and/or +2 and/or +3 and/or +4 and/or +5 valence compounds.

Example 47

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 43. The samples were fired at 1100°C. for 1 hour. The photographs of samples are shown in FIGS. 17( a) to17(d).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith 1 wt %, 10 wt % and 50 wt % glass starting materials (SPCN) exhibitimproved sintering ability during the heat treatment. The samples addedwith the sintering additives still hold their shapes after the heattreatment. However, the calcium sulfate without the glass startingmaterials collapses after the heat treatment (see FIG. 17( a)). Itindicates that the sintering ability of calcium sulfate can be improvedby adding various amounts (1 wt %, 10 wt % and 50 wt %) of glassstarting materials. The glass starting materials are selected from +1and/or +2 and/or +3 and/or +4 and/or +5 valence compounds.

Example 48

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 44. The samples were fired at 1200°C. for 1 hour. The photographs of samples are shown in FIGS. 18( a) to18(d).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith 1 wt %, 10 wt % and 50 wt % glass starting materials (SPCN) exhibitimproved sintering ability during the heat treatment. The samples addedwith the sintering additives still hold their shapes after the heattreatment. However, the calcium sulfate without the glass startingmaterials collapses after the heat treatment (see FIG. 18( a)). Itindicates that the sintering ability of calcium sulfate can be improvedby adding various amounts (1 wt %, 10 wt % and 50 wt %) of glassstarting materials. The glass starting materials are selected from +1and/or +2 and/or +3 and/or +4 and/or +5 valence compounds.

Examples 49 to 52

The cylinder samples for these examples of the present invention wereprepared using the same methods as in EXAMPLES 41 to 44. The sampleswere made into cylinder of 10 mm diameter and 10 mm height. The sampleswere fired at 900° C. to 1200° C. for 1 hour. After firing, the sampleswere then ground to obtain flat surfaces. The compressive strength ofcylinder samples was measured by using the instrument (MTS810, MTS, USA)at the room temperature. The displacement rate was 0.96 mm/min. Thecompressive strength of samples is presented in the Table 11.

TABLE 11 CaSO₄ + 1 wt % glass CaSO₄ + 10 wt % CaSO₄ + 50 wt % startingglass starting glass starting materials (1 wt materials (10 wt materials(50 wt % CaSO₄ % SPCN) % SPCN) SPCN) EXAMPLE  900° C./ / 80 ± 3 42 ± 149 ± 1 49 compressive strength (MPa) EXAMPLE 1000° C./ / 171 ± 3  119 ±10 26 ± 1 50 compressive strength (MPa) EXAMPLE 1100° C./ / 126 ± 7  157± 21 12 ± 1 51 compressive strength (MPa) EXAMPLE 1200° C./ / 42 ± 3  86± 10  7 ± 1 52 compressive strength (MPa) /: The compressive strength ofsamples cannot be measured due to the collapse of the samples.

Hereinbefore, the EXAMPLES show that the compressive strength of purecalcium sulfate (CaSO₄) cannot be measured owing to the collapse ofsamples. It indicates that the pure calcium sulfate cannot be sinteredby using the heat treatment. However, the compressive strength ofCaSO₄-based samples is increased via adding 1 wt %, 10 wt % and 50 wt %glass starting materials. The glass starting materials are selected from+1 and/or +2 and/or +3 and/or +4 and/or +5 valence compounds. By usingthe suitable sintering profile, the compressive strength of calciumsulfate added with the sintering additives is around 171 MPa. Itsuggests that the sintering ability of calcium sulfate can be improvedby adding various amounts of glass starting materials as sinteringadditives.

Hereinbefore, the EXAMPLES reveal that the sintering ability of calciumsulfate can be improved by adding four kinds of additives. Theseadditives may form glass during sintering, and are thus referred to asglass starting materials. Glass is a amorphous solid which itscrystalline structure is lacking of long-range order. As severalmetallic componds or metallic oxides are heated at the elevatedtemperature, the metallic ions may not have enough time to form thelong-range order. Amorphous phase is then formed. As some fine crystalsare formed and dispersed within the glassy matrix, the material is alsotermed as the glass-ceramics. The glass and glass-ceramic materials canflow at elevated temperature. The addition of suitable glass orglass-ceramic can assist the densification of ceramics. Hereinafter, theEXAMPLES reveal that the sintering ability of calcium sulfate can beimproved by adding two or more than two kinds of glass startingmaterials. All the materials used for these EXAMPLES are calciumsulfate, +1 valence glass starting material (such as sodium hydrogencarbonate, NaHCO₃), +2 valence glass starting material (such as calciumoxide, CaO), +4 valence glass starting material (such as silica, SiO₂)and +5 valence glass starting material (such as phosphorous pentoxide,P₂O₅). These additives easily form a glass or a glass-ceramic duringsintering

Examples 53 to 57

In these EXAMPLES of the present invention, CaSO₄ and glass startingmaterials were first mixed together. The amount of glass startingmaterials was 1 wt %. The mixed powders were consolidated into cylindersof 10 mm diameter and 10 mm height. The glass starting materials wereselected from +1 valence glass starting materials (e.g. sodium hydrogencarbonate, NaHCO₃), +2 valence glass starting materials (e.g. calciumoxide, CaO), +4 valence glass starting materials (e.g. silica, SiO₂) and+5 valence glass starting materials (e.g. phosphorus pentoxide, P₂O₅).The compositions of glass starting materials are listed in the Table 12.

TABLE 12 Compositions 1 wt % glass starting materials, 0.8 wt % SiO₂ +0.2 wt % P₂O₅ labeled as 1 wt % SP 1 wt % glass starting materials, 0.71wt % SiO₂ + 0.13 wt % P₂O₅ + labeled as 1 wt % SPN 0.16 wt % NaHCO₃ 1 wt% glass starting materials, 0.59 wt % SiO₂ + 0.15 wt % P₂O₅ + labeled as1 wt % SPC 0.26 wt % CaO 1 wt % glass starting materials, 0.56 wt %SiO₂ + 0.11 wt % P₂O₅ + labeled as 1 wt % SPCN 0.21 wt % CaO + 0.12 wt %NaHCO₃

The samples were fired at 900° C. to 1200° C. for 1 hour. The densitiesof samples were recorded after firing, as shown in the Table 13.

TABLE 13 CaSO₄ + 1 wt CaSO₄ + 1 wt CaSO₄ + 1 wt CaSO₄ + 1 wt % glass %glass % glass % glass starting starting starting starting materialsmaterials materials materials CaSO₄ (SP) (SPN) (SPC) (SPCN) EXAMPLE  25°C. 2.1 1.9 1.9 1.9 1.9 53 density (g/cm³) EXAMPLE  900° C. / 2.0 2.4 1.92.2 54 density (g/cm³) EXAMPLE 1000° C. / 2.4 2.8 2.3 2.7 55 density(g/cm³) EXAMPLE 1100° C. / 2.8 2.7 2.8 2.8 56 density (g/cm³) EXAMPLE1200° C. / 2.7 2.6 2.7 2.5 57 density (g/cm³)

Hereinbefore, the examples show that the density of calcium sulfate(CaSO₄) added with two or more than two glass starting materials isincreased after the heat treatment. It indicates that after the heattreatment, the sintering ability of calcium sulfate can be improved byadding two or more glass starting materials selected from +1 and/or +2and/or +3 and/or +4 and/or +5 valence compounds. It also means thatadding SiO₂ and/or NaHCO₃ and/or CaO and/or P₂O₅ can assist thedensification of calcium sulfate.

Example 58

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 54. The samples were fired at 900°C. for 1 hour. The photographs of samples are shown in FIGS. 19( a) to19(e).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith two or more than two kinds of glass starting materials exhibitimproved sintering ability during the heat treatment. The combinationsof glass starting materials are selected from NaHCO₃, CaO, SiO₂ andP₂O₅. The samples added with the glass starting materials still holdtheir shapes after the heat treatment. However, the calcium sulfatewithout the glass starting materials collapses after the heat treatment(see FIG. 19( a)). It indicates that the sintering ability of calciumsulfate can be improved by adding two or more than two kinds of glassstarting materials selected from +1 and/or +2 and/or +3 and/or +4 and/or+5 valence compounds.

Example 59

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 55. The samples were fired at 1000°C. for 1 hour. The photographs of samples are shown in FIGS. 20( a) to20(e).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith two or more than two kinds of glass starting materials exhibitimproved sintering ability during the heat treatment. The combinationsof glass starting materials are selected from NaHCO₃, CaO, SiO₂ andP₂O₅.

The samples added with the glass starting materials still hold theirshapes after the heat treatment. However, the calcium sulfate withoutthe glass starting materials collapses after the heat treatment (seeFIG. 20( a)). It indicates that the sintering ability of calcium sulfatecan be improved by adding two or more than two kinds of glass startingmaterials selected from +1 and/or +2 and/or +3 and/or +4 and/or +5valence compounds.

Example 60

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 56. The samples were fired at 1100°C. for 1 hour. The photographs of samples are shown in FIGS. 21( a) to21(e).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith two or more than two kinds of glass starting materials exhibitimproved sintering ability during the heat treatment. The combinationsof glass starting materials are selected from NaHCO₃, CaO, SiO₂ andP₂O₅. The samples added with the glass starting materials still holdtheir shapes after the heat treatment. However, the calcium sulfatewithout the glass starting materials collapses after the heat treatment(see FIG. 21( a)). It indicates that the sintering ability of calciumsulfate can be improved by adding two or more than two kinds of glassstarting materials selected from +1 and/or +2 and/or +3 and/or +4 and/or+5 valence compounds.

Example 61

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 57. The samples were fired at 1200°C. for 1 hour. The photographs of samples are shown in FIGS. 22( a) to22(e).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith two or more than two kinds of glass starting materials exhibitimproved sintering ability during the heat treatment. The combinationsof glass starting materials are selected from NaHCO₃, CaO, SiO₂ andP₂O₅. The samples added with the glass starting materials still holdtheir shapes after the heat treatment. However, the calcium sulfatewithout the glass starting materials collapses after the heat treatment(see FIG. 22( a)). It indicates that the sintering ability of calciumsulfate can be improved by adding two or more than two kinds of glassstarting materials selected from +1 and/or +2 and/or +3 and/or +4 and/or+5 valence compounds.

Examples 62 to 65

The cylinder samples for these examples of the present invention wereprepared using the same methods as in EXAMPLES 54 to 57. The sampleswere made into cylinders of 9 mm diameter and 9 mm height. The sampleswere fired at 900° C. to 1200° C. for 1 hour. After firing, the sampleswere then ground to obtain flat surfaces. The compressive strength ofcylinder samples was measured by using the universal testing instrument(MTS810, MTS, USA) at the room temperature. The displacement rate was0.96 mm/min. The compressive strength of samples is presented in theTable 14.

TABLE 14 CaSO₄ + 1 wt CaSO₄ + 1 wt CaSO₄ + 1 wt CaSO₄ + 1 wt % glass %glass % glass % glass starting starting starting starting materialsmaterials materials materials CaSO₄ (SP) (SPN) (SPC) (SPCN)EXAMPLE >900° C./ / 10 ± 6 87 ± 5 11 ± 1 80 ± 3 62 compressive strength(MPa) EXAMPLE 1000° C./ / 62 ± 7 184 ± 7   52 ± 10 171 ± 3  63compressive strength (MPa) EXAMPLE 1100° C./ / 128 ± 17 103 ± 8  155 ±6  126 ± 7  64 compressive strength (MPa) EXAMPLE 1200° C./ / 92 ± 9 61± 3 77 ± 4 42 ± 3 65 compressive strength (MPa) /: The compressivestrength of samples cannot be measured due to the collapse of thesamples.

Hereinbefore, the examples show that the compressive strength of purecalcium sulfate (CaSO₄) cannot be measured owing to the collapse ofsamples. It indicates that the pure calcium sulfate cannot be sinteredby using the heat treatment. However, the compressive strength ofCaSO₄-based samples is increased by adding two or more than two kinds ofglass starting materials as sintering additives. In the appropriatecondition, the compressive strength of calcium sulfate added with thesintering additives is around 184 MPa. It suggests that the sinteringability of calcium sulfate can be improved by adding two or more thantwo kinds of sintering additives (glass starting materials). The glassstarting materials are selected from +1 and/or +2 and/or +3 and/or +4and/or +5 and/or valence glass starting materials.

Example 66

For the present EXAMPLE, firstly, CaSO₄ and glass starting materialswere first mixed together. The amount of glass starting materials was14.5 wt %. The mixed powders were consolidated into cylinders of 25.4 mmdiameter and 3 mm height. The glass starting materials were selectedfrom +3 valence glass starting materials (e.g. aluminum oxide, Al₂O₃)and +4 valence glass starting materials (e.g. silica, SiO₂). Thecompositions of glass starting materials are listed in the Table 15.

TABLE 15 Compositions 14.5 wt % glass starting materials, 5 wt % SiO₂ +9.5 wt % Al₂O₃ labeled as SA

The samples were fired at 1100° C. for 3 hours. The densities of sampleswere recorded after firing, as shown in the Table 16.

TABLE 16 CaSO₄ + 14.5 wt % glass CaSO₄ starting materials (SA) EXAMPLE66 1100° C. / 1.7 density (g/cm³) /: The densities of samples cannot bemeasured due to the collapse of the samples.

Hereinbefore, the example shows that the density of calcium sulfate(CaSO₄) added with two kinds of glass starting materials is increasedafter the suitable heat treatment. It indicates that after the heattreatment, the sintering ability of calcium sulfate can be improved byadding two kinds of glass starting materials selected from +1 and/or +2and/or +3 and/or +4 and/or +5 valence compounds. It also suggests thatadding SiO₂ and Al₂O₃ can assist the densification of calcium sulfate.

Example 67

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 66. The samples were fired at 1100°C. for 3 hours. The photographs of samples are shown in FIGS. 23( a) to23(b).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith two kinds of glass starting materials exhibit improved sinteringability during the heat treatment. The samples added with the glassstarting materials still hold their shapes after the heat treatment.However, the calcium sulfate without the glass starting materialscollapses after the heat treatment (see FIG. 23( a)). It indicates thatthe sintering ability of calcium sulfate can be improved by adding twokinds of glass starting materials selected from +1 and/or +2 and/or +3and/or +4 and/or +5 valence compounds. The glass starting materials areselected from +3 valence glass starting materials (e.g. Al₂O₃) and +4valence glass starting materials (e.g. SiO₂)

Example 68

The disc samples for these EXAMPLES of the present invention wereprepared using the same methods as in EXAMPLE 66. The samples were firedat 1100° C. for 3 hours. The samples were then ground to obtain flatsurfaces firstly. The flexural strength of disc samples were measured byusing the biaxial 4-ball bending test (instrument: MTS810, MTS Co., USA)at the room temperature. The displacement rate was 0.48 mm/min. Theflexural strength of samples is presented in the Table 17.

TABLE 17 CaSO₄ + 14.5 wt % glass starting CaSO₄ materials (SA) EXAMPLE68 flexural / 20 ± 1 strength (MPa) /: The flexural strength of samplescannot be measured due to the collapse of the samples.

Hereinbefore, the example shows that the flexural strength of purecalcium sulfate (CaSO₄) cannot be measured owing to the collapse ofsamples. It indicates that the pure calcium sulfate cannot be sinteredby using the heat treatment. However, the flexural strength ofCaSO₄-based samples is increased by adding two kinds of glass startingmaterials as sintering additives. It suggests that the sintering abilityof calcium sulfate can be improved by adding two kinds of sinteringadditives (or glass starting materials) selected from +1 and/or +2and/or +3 and/or +4 and/or +5 valence compounds. The glass startingmaterials used for EXAMPLE 68 are Al₂O₃ and SiO₂.

Hereinbefore, the EXAMPLES reveal that the sintering ability of calciumsulfate can be improved by adding two or more than two kinds of glassstarting materials as sintering additives. The glass starting materialsused for the present invention are selected from +1 and/or +2 and/or +3and/or +4 and/or +5 valence glass starting materials. Hereinafter, theEXAMPLES reveal that the sintering ability of calcium sulfate can alsobe improved by adding one glass starting material. The materials used inthe following EXAMPLES are calcium sulfate powders and +4 valence glassstarting material (silica, SiO₂). The +4 valence glass starting materialis used as the sintering additive.

Example 69

The materials used in the following EXAMPLES were calcium sulfate powderand +4 valence glass starting material (silica, SiO₂). Firstly, CaSO₄and +4 valence glass starting materials (SiO₂) were first mixedtogether. The amounts of glass starting materials were 1 wt %, 10 wt %and 50 wt %. The mixed powders were consolidated into cylinders of 25.4mm diameter and 3 mm height. The samples were fired at 1100° C. for 3hours. The densities of samples were recorded after firing, as shown inthe following Table 18.

TABLE 18 CaSO₄ + 1 wt % CaSO₄ + 10 CaSO₄ + 50 CaSO₄ SiO₂ wt % SiO₂ wt %SiO₂ 1100° C. / 2.7 1.6 1.9 density (g/cm³) /: The densities of samplescannot be measured due to the collapse of the samples.

Hereinbefore, the EXAMPLE shows that the density of calcium sulfate(CaSO₄) added with 1 wt %, 10 wt % and 50 wt % glass starting materialsis increased after the suitable heat treatment. It indicates that afterthe heat treatment, the sintering ability of calcium sulfate can beimproved by adding various amounts (1 wt %, 10 wt % and 50 wt %) of +4valence glass starting materials (e.g. SiO₂). It also means that addingvarious amounts of +4 valence glass starting materials can assist thedensification of calcium sulfate.

Example 70

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 69. The samples were fired at 1100°C. for 3 hours. The photographs of samples are shown in FIGS. 24( a) to24(d).

Hereinbefore, the EXAMPLE shows that the calcium sulfate samples addedwith 1 wt %, 10 wt % and 50 wt % +4 valence glass starting materials(SiO₂) exhibit improved sintering ability during the heat treatment. Thesamples added with various amounts of glass starting materials stillhold their shapes after the heat treatment. However, the calcium sulfatewithout the glass starting materials collapses after the heat treatment(see FIG. 24( a)). It indicates that the sintering ability of calciumsulfate can be improved by adding various amounts of +4 valence glassstarting materials. Hereinbefore, the EXAMPLE reveals that the sinteringability of calcium sulfate can be improved by adding one kind ofsintering additives selected from +1 or +2 or +3 or +4 or +5 valencecompounds.

Example 71

The samples for this EXAMPLE of the present invention were preparedusing the same method as in EXAMPLE 43. The compositions of samples werecalcium sulfate added with 1 wt % glass starting materials. The glassstarting materials comprised 0.56 wt % SiO₂, 0.11 wt % P₂O₅, 0.21 wt %CaO and 0.12 wt % NaHCO₃. The samples were fired at 1100° C. for 1 hour.The SEM micrograph of sample is shown in FIG. 25. It can be found thatthe sample is dense after firing.

Hereinbefore, the EXAMPLE reveals that the calcium sulfate added fouradditives (NaHCO₃, CaO, SiO₂ and P₂O₅) exhibits improved sinteringability during firing. It indicates that the sintering ability ofcalcium sulfate can be improved by adding four kinds of glass startingmaterials selected from +1 and/or +2 and/or +3 and/or +4 and/or +5valence compounds.

Examples 72 to 78

The samples for these EXAMPLES of the present invention were preparedusing the same method as in EXAMPLE 43. The samples comprised calciumsulfate and 1 wt % glass starting materials (SP, SPN, SPC and SPCN),wherein SP is the combination of SiO₂ and P₂O₅; SPN is the combinationof SiO₂, P₂O₅ and NaHCO₃, SPC is the combination of SiO₂, P₂O₅ and CaO;and SPCN is the combination of SiO₂, P₂O₅, CaO and NaHCO₃. The sampleswere fired at 1100° C. for 1 hour. After firing, the samples were placedinto the test tube with normal saline, and then, the test tubes were putinto the water bath at a temperature of 37.5° C. The ratio of sample tonormal saline was 1 to 10. The pH value of samples was recorded for 7days, as shown in the Table 19. The pH value of normal saline wasrecorded for the purpose of comparison.

TABLE 19 CaSO₄ + 1 wt CaSO₄ + 1 wt CaSO₄ + 1 wt CaSO₄ + 1 wt % glass %glass % glass % glass starting starting starting starting Normalmaterials materials materials materials saline (SP) (SPN) (SPC) (SPCN)EXAMPLE 1^(st) day's 5.3 6.1 6.2 6.2 6.2 72 pH EXAMPLE 2^(nd) day's 5.46.3 6.3 6.5 6.5 73 pH EXAMPLE 3^(rd) day's 5.3 6.5 6.4 6.6 6.6 74 pHEXAMPLE 4^(th) day's 5.3 6.4 6.3 6.6 6.5 75 pH EXAMPLE 5^(th) day's 5.46.6 6.5 6.7 6.6 76 pH EXAMPLE 6^(th) day's 4.7 6.4 6.3 6.6 6.5 77 pHEXAMPLE 7^(th) day's 4.8 6.4 6.2 6.5 6.4 78 pH

Hereinbefore, the EXAMPLES reveal that after firing, the pH value ofcalcium sulfate added with two or more than two kinds of sinteringadditives (glass starting materials) is around 6.1 to 6.7, which islocated in the range of human body's pH (6 to 8). It indicates thatafter firing, the pH value of calcium sulfate added with sinteringadditives is located in the range of human body's pH. The sinteringadditives used for the present invention are selected from +1 and/or +2and/or +3 and/or +4 and/or +5 valence compounds, such as SiO₂ and/orP₂O₅ and/or CaO and/or NaHCO₃. These sintering additives can form glassor glass ceramic during sintering. The glass or glass ceramic assiststhe densification of calcium sulfate. The presence of the glass orglass-ceramic is stable in body fluid.

Example 79

The samples for the EXAMPLE of the present invention were prepared usingthe same method as in EXAMPLE 43. The samples comprised of calciumsulfate and 1 wt % glass starting materials (SP, SPN, SPC and SPCN). Thesamples were fired at 1100° C. for 1 hour. After firing, thecytotoxicity of samples was determined by MTT (microculture tetrazolium,3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay.First, the powder of samples was immersed in the medium for extraction.They were placed in the incubator for 24 hours. The test tubes were thencentrifuged, and the supernatant aqueous solution was collected. Thesolution was then filtered by 0.22 μm aseptic filtering membrane. Inaddition, the cultured L929 cells were seeded into 96-well culture dish.The cell density of each well was 10⁴ cells/mL. The cells were thenincubated for 24 hours. After the treatment, the extracted solution wasdropped into each well, and then, the further 24-hour incubation wascarried out. After that, the extracted solution was removed, and newmedium and MTT working solution were dropped into each well. Afterincubating for 4 hours, the dimethyl sulfoxide (DMSO) solution wasdropped. The absorption of light with 540 nm wavelength in each well wasmeasured by an optical spectroscopy (ELISA Co.) reader. The viability ofsamples is shown in the Table 20.

TABLE 20 CaSO₄ + CaSO₄ + CaSO₄ + CaSO₄ + 1 wt 1 wt 1 wt 1 wt % glass %glass % glass % glass starting starting starting starting DMSO materialsmaterials materials materials (dimethyl (SP) (SPN) (SPC) (SPCN)sulfoxide) viability (%) 80 ± 6 88 ± 7 101 ± 14 102 ± 12 4 ± 2The DMSO (dimethl sulfoxide) is the positive control. It is toxic andharmful to cells.

Hereinbefore, the EXAMPLES reveal that after firing, viability ofcalcium sulfate added two or more than two kinds of sintering additives(glass starting materials) is higher than 80%. It indicates that afterfiring, calcium sulfate added with sintering additives shows goodresults of viability. The sintering additives used for the presentinvention are selected from +1 and/or +2 and/or +3 and/or +4 and/or +5valence compounds, such as SiO₂ and/or P₂O₅ and/or CaO and/or NaHCO₃.These sintering additives can form glass or glass ceramic duringsintering. The glass or glass ceramic assists the densification ofcalcium sulfate. The glass or glass ceramic is not toxic to cells.

While the invention has been described by way of examples and in termsof preferred embodiments, it is to be understood that the invention isnot limited thereto. To the contrary, it is intended to cover variousmodifications. Therefore, the scope of the appended claims should beaccorded the broadest interpretation so as to encompass all suchmodifications.

1. A sinterable calcium sulfate ceramic material consisting of calciumsulfate and a sintering additive.
 2. The sinterable calcium sulfateceramic material in accordance with claim 1, wherein the sinteringadditive is selected from the group consisting of a +1 valence elementand a compound thereof, a +2 valence element and a compound thereof, a+3 valence element and a compound thereof, a +4 valence element and acompound thereof and a +5 valence element and a compound thereof.
 3. Thesinterable calcium sulfate ceramic material in accordance with claim 1,wherein the sintering additive is selected from the group consisting ofthe +1 valence element and the compound thereof containing a sodium (Na)element and the compound thereof.
 4. The sinterable calcium sulfateceramic material in accordance with claim 3, wherein the +1 valenceelement and the compound thereof contain sodium hydrogen carbonate(NaHCO₃).
 5. The sinterable calcium sulfate ceramic material inaccordance with claim 1, wherein the sintering additive is selected fromthe group consisting of the +2 valence element and the compound thereofcontaining a calcium (Ca) element and the compound thereof.
 6. Thesinterable calcium sulfate ceramic material in accordance with claim 5,wherein the +2 valence element and the compound thereof contain calciumoxide (CaO).
 7. The sinterable calcium sulfate ceramic material inaccordance with claim 1, wherein the sintering additive is selected fromthe group consisting of the +3 valence element and the compound thereofcontaining an aluminum (Al) element and the compound thereof.
 8. Thesinterable calcium sulfate ceramic material in accordance with claim 7,wherein the +3 valence element and the compound thereof contain aluminumoxide (Al₂O₃).
 9. The sinterable calcium sulfate ceramic material inaccordance with claim 1, wherein the sintering additive is selected fromthe group consisting of the +4 valence element and the compound thereofcontaining a silicon (Si) element and the compound thereof or azirconium (Zr) element and the compound thereof.
 10. The sinterablecalcium sulfate ceramic material in accordance with claim 9, wherein the+4 valence element and the compound thereof contain silica (SiO₂) orzirconium oxide (ZrO₂).
 11. The sinterable calcium sulfate ceramicmaterial in accordance with claim 1, wherein the sintering additive isselected from the group consisting of the +5 valence element and thecompound thereof containing a phosphorus (P) element and the compoundthereof.
 12. The sinterable calcium sulfate ceramic material inaccordance with claim 11, wherein the +5 valence element and thecompound thereof contain phosphorus pentoxide (P₂O₅).
 13. The sinterablecalcium sulfate ceramic material in accordance with claim 1, wherein theweight ratio of the sintering additive to the calcium sulfate rangesfrom 0.5% to 50%.
 14. The sinterable calcium sulfate ceramic material inaccordance with claim 1, wherein a sintering temperature of the calciumsulfate ceramic material is above 900° C.
 15. The sinterable calciumsulfate ceramic material in accordance with claim 1, wherein a flexuralstrength of the calcium sulfate ceramics after sintering is equal to orhigher than 90 MPa, and a compressive strength of the calcium sulfateceramic material after sintering is equal to or higher than 184 MPa. 16.The sinterable calcium sulfate ceramic material in accordance with claim1, wherein the sintering additive is a glass starting material which canform a glass or a glass-ceramic material during sintering.
 17. A methodof manufacturing a sinterable calcium sulfate ceramic material, themethod comprising: providing calcium sulfate; and mixing a sinteringadditive with the calcium sulfate to prepare a mixture; and shaping themixture in a mold to form a product; and firing the product at atemperature ranging from 600° C. to 1400° C. to form the sinterablecalcium sulfate ceramic material.
 18. The method in accordance withclaim 17, wherein the sintering additive is selected from the groupconsisting of a +1 valence element and a compound thereof, a +2 valenceelement and a compound thereof, a +3 valence element and a compoundthereof, a +4 valence element and a compound thereof and a +5 valenceelement and a compound thereof.
 19. The method in accordance with claim18, wherein a weight ratio of the sintering additive to the calciumsulfate ranges from 0.5% to 50%.
 20. The method in accordance with claim18, wherein the sintering additive is a glass starting material whichcan form a glass or a glass-ceramic material during sintering.